This section provides background information related to the present disclosure which is not necessarily prior art.
The design and manufacture of a structure requires the selection of appropriate materials for structural components or device substructures. To select a suitable material, scientists, engineers, designers, architects, etc., require specific knowledge of the material such as the stress and strain the material is able to withstand before failing. Most materials exhibit rate-dependent properties and many applications expose materials to both low and high strain rate loading.
Various measurement devices have been developed for testing and quantifying the physical properties and stress characteristics of materials. For example, a Split-Hopkinson pressure bar may be used to test the dynamic stress-strain response of materials. During use of a Split-Hopkinson pressure bar, a specimen or test sample is placed between, and physically contacts, an incident bar and a transmission bar. At a first end of the incident bar away from the specimen, a stress wave, pressure wave, or incident wave is created using a striker bar. The incident wave propagates through the incident bar from the first end toward a second end that physically contacts the specimen. Upon reaching the specimen, a first portion of the energy from the incident wave travels through the specimen while a second portion is reflected away from the specimen and back through the incident bar. The first portion of the wave travels through, stresses, and deforms the specimen, and is then transferred to the transmission bar that physically contacts the specimen. Movement of the transmission bar may be stopped by a momentum bar and a momentum trap.
When the first and second portions of the incident wave reach the ends of the incident bar and the transmission bar respectively, the portions of the incident wave reflect off the ends of the bars and rapidly travel back and forth through the bars multiple times. Each time the incident wave reaches the specimen end of the bars, a portion of the incident wave energy is transferred to the specimen, which is again subjected to increased stresses. These transits of the incident wave back and forth through the incident bar and the transmission bar, and thus through the specimen, create a stepping motion and a non-constant strain rate in the specimen. A Split-Hopkinson pressure bar measurement is therefore valid only during the first motion step, but many materials will not have failed during that first motion step.
Additionally, the operational and failure characteristics of elastic materials such as vulcanizates (e.g., natural rubbers), elastomers (e.g., silicones, polymers), etc., are important considerations in selecting materials for use as sealers, barriers, vibration dampeners, shock absorbers and cushioners, as well as other uses. The Split-Hopkinson pressure bar subjects a test sample between the incident bar and the transmission bar to a compressive force as the incident wave travels through the test sample. The Split-Hopkinson pressure bar may thus test materials in tension, but does not function well for specimens that have a high strain to failure. Further, testing of a specimen using the Split-Hopkinson pressure bar subjects the material to a non-constant strain rate as the incident wave propagates back and forth through the incident bar and the transmission bar. The Split-Hopkinson pressure bar thus provides a high strain rate but not a high strain. Other devices using servo-mechanical methods may provide high strain but not a high strain rate.
A device that is suitable for measuring various characteristics such as tensile strength and failure stresses at a constant strain rate of various materials such as flexible, pliable, and ductile materials, as well as other materials, that provides both a high strain rate and high strain, would be a welcome addition to the art.